Towards an Atlas of Human Helminth Infection in sub-saharan Africa: The Use of Geographical Information Systems (GIS) S. Brooker, M. Rowlands, L. Haller, L. Savioli and D.A.P. Bundy * *Ndir, O. et al. (1996) Enquete Nationale sur la Bilharziose au Senegal. Universite Cheikh anta Diop de Dakar. Simon Brooker, Megan Rowlands, Laurence Haller and Don Bundy are at the WHO Collaborating Centre, Wellcome Trust Centre for the Epidemiology of Infectious Disease, University of Oxford, South Parks Road, Oxford, UK OX1 3FY. Lorenzo Savioli is at the World Health Organization, 1211, Geneva 27, Switzerland. Tel: +44 1865 281232, Fax: +44 1865 281245, e-mail: simon.brooker@ceid.ox.ac.uk Parasitology Today, vol. 16, no. 7, 2000 0169-4758/00/$ see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S0169-4758(00)01687-2 303
Table 1. An African helminth database for sub-saharan Africa a,b No. No. No. of admin % of admin units for which there are data Country refs surveys units in country Schistosomiasis Geohelminths Both Angola c 3 39 48 10.4 2.1 0.0 Benin 6 60 77 16.9 2.6 1.3 Botswana 10 179 10 80.0 30.0 30.0 Burkina Faso 19 75 301 15.6 0.3 0.3 Burundi 8 16 15 26.7 13.3 13.3 C.A.R. 6 50 51 45.1 45.1 45.1 Cameroon 28 143 49 100.0 100.0 100.0 Congo 20 80 46 17.4 4.3 4.3 DR Congo 7 95 38 18.4 13.2 13.2 Equatorial Guinea c 2 5 7 0.0 14.3 0.0 Ethiopia 50 234 94 20.7 12.4 12.4 Eritrea d 2 2 38 0.0 0.0 0.0 Gabon 13 47 46 15.2 2.2 0.0 Gambia 6 14 37 2.7 8.1 2.7 Ghana c 11 57 10 30.0 70.0 20.0 Guinea 4 25 33 36.4 36.4 36.4 Guinea Bissau 1 1 37 0.0 2.7 0.0 Ivory coast 17 76 50 36.0 18.0 12.0 Kenya 45 88 47 29.8 25.5 21.3 Liberia 10 83 54 7.4 24.1 3.7 Madagascar 28 286 111 21.6 15.3 15.3 Malawi 4 42 24 83.3 4.2 0.0 Mali 24 579 46 78.3 4.3 4.3 Mauritania 8 93 44 56.8 4.5 4.5 Mozambique 4 4 128 4.7 0.7 0.0 Namibia c 6 28 26 11.5 11.5 11.5 Niger 16 57 35 31.4 5.7 5.7 Nigeria c 54 156 31 48.4 48.4 41.9 Rwanda c 3 5 10 10.0 20.0 10.0 Senegal 15 300 30 80.0 10.0 10.0 Sierra Leone 9 23 15 53.3 13.3 13.3 Somalia c 13 39 16 25.0 25.0 18.8 Sudan 10 50 18 27.8 5.6 5.6 Tanzania 55 110 97 38.1 37.1 25.8 Tchad 3 9 14 42.9 28.6 28.6 Togo c 4 66 5 80.0 20.0 20.0 Uganda 26 91 46 71.7 56.5 60.9 Zambia 23 97 97 19.6 4.1 4.1 Zimbabwe 14 119 57 94.7 5.3 5.3 Total 583 3486 2304 29.7 14.9 12.6 a This work in progress has currently identified data from 39 countries. Where possible, the prevalence data are associated with a specific district within a country, but see c. b Countries in North Africa were not included because of the concentration of disease burden as a result of helminth infection in sub-saharan Africa. South Africa, Swaziland and Lesotho are temporarily excluded while we await publication of a separate GIS analysis of helminths for these countries. c The administrative unit is the region. d Not possible to assign survey data to specific admin units. 304 Parasitology Today, vol. 16, no. 7, 2000
Table 2. Independent estimates of prevalence of the major helminth infections in sub-saharan Africa a over the past 50 years S. haematobium S. mansoni A. lumbricoides T. trichiura Hookworm b Stoll (1947) 17 26.5 15.5 39.9 18.9 33.1 Crompton and Tulley (1987) 14 32.3 Utroska et al. (1989) 15 25.5 c Bundy et al. (1998) 3 20.3 16.6 26.9 Weighted current estimates d Prevalence (%) 25.9 18.3 26.7 20.9 33.0 Total number surveyed 827 986 672 057 361166 317 359 394 983 Prevalence in school-aged 27.4 14.0 30.2 29.5 32.1 children (%) Number of school-aged 514 679 330 533 165 599 136 331 190 932 children surveyed Cases (million) e 131 98 161 100 192 a Defined as the Global Burden of Disease Study 3, but excludes South Africa, Swaziland and Lesotho. b Both Necator americanus and Anclyostoma duodenale. c Combined Schistosoma haematobium and S. mansoni. d Estimates are for both sexes combined. Estimates are based on prevalences for each country in the database. e Based on 2000 population estimates [US Census Bureau (1999). International Data Base]. * * Parasitology Today, vol. 16, no. 7, 2000 305
Fig. 1. Maps are shown detailing geohelminths in Africa: Ascaris, Trichuris and hookworm by district (a) and schistosomiasis in Africa: Schistosoma mansoni and S. haematobium by district (b). The geohelminth species with the highest prevalence is taken to represent the prevalence of geohelminth infection. Similarly, the schistosome species with the highest prevalence is taken to represent the total prevalence of schistosome infection. The maps show data for sub-saharan Africa only. Of the 2304 administrative units (usually districts) in 39 countries, data are available for schistosomiasis in 684 (29.7%) and for geohelminths in 343 (14.9%). However, the population in Africa is not homogeneously distributed, and many of the districts for which no data are currently available also have low-density populations. To highlight the high population density areas of Africa we have created a template that masks out all districts with population density 5 people per km 2 and between 5 and 20 people per km 2. The atlas is also available at http://www.ceid.ox.ac.uk/child/. 306 Parasitology Today, vol. 16, no. 7, 2000
Acknowledgements The atlas is a work in progress and hence the estimates provided are preliminary. Revision and improvement require further information on the prevalence of infection within countries. If you know of relevant data that could be included, or if you would like to be a partner in this initiative, then please contact the WHO in Geneva. Collaborating partners include the Strategy Development and Monitoring for Parasitic Diseases and Vector Control, Communicable Disease Control, Prevention and Eradication, World Health Organization, 1211, Geneva 27 (Dirk Engels, Lester Chitsulo and Antonio Montreso); the WHO/UNICEF Joint Programme on Health Mapping and GIS, HealthMap (Kathy O Neill, Jean-Pierre Meert and Isabelle Nutall); and the Partnership for Child Development and the International School Health Initiative of the World Bank. The Partnership is supported by the United Nations Development Programme, the Rockefeller Foundation, the Edna McConnell Clark Foundation, the James S. McDonnell Foundation, the Wellcome Trust, the World Bank, UNICEF, and the WHO. SB is in receipt of a Wellcome Trust Prize Studentship. DAPB acknowledges the financial support of the Wellcome Trust. We are grateful to Andrew Hall, Simon Hay and Edwin Michael for useful discussions and comments, and thank Michael Beasley and Jonathan Toomer for invaluable assistance in data preparation. Microsatellite Markers and Genetic Mapping in Plasmodium falciparum Michael Ferdig and Xin-zhuan Su are at the Laboratory of Parasitic Diseases, National Institutes of Health, 4 Center Drive 0425, Bethesda, MD 20892-0425, USA. Tel: +1 301 496 4023, Fax: +1 301 402 0079, e-mail: xsu@helix.nih.gov M.T. Ferdig and X-z. Su Parasitology Today, vol. 16, no. 7, 2000 0169-4758/00/$ see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S0169-4758(00)01676-8 307